Process for the preparation of taxan derivatives

ABSTRACT

A process for the preparation of the compound 13-(N-Boc-β-isobutylisoserinyl)-14β-hydroxybaccatine III 1,14-carbonate.

[0001] The present invention relates to a process for the preparation ofthe compound 13-(N-Boc-β-isobutylisoserinyl)-14β-hydroxybaccatine III1,14-carbonate, of formula (I):

[0002] Compound (I), disclosed in PCT WO 01/02407, is particularlyactive against breast, lung, ovary, colon, prostate, kidney and pancreastumors, as well as against cells resistant to known antitumor agents,such as adriamycin, vinblastine and some Pt derivatives.14β-Hydroxy-1,14-carbonate-deacetylbaccatine III derivatives are usuallyprepared starting from the precursor 14β-hydroxy-deacetylbaccatine III,a natural compound obtainable in small amounts by extraction of Taxuswallichiana leaves, as disclosed in EP 559,019. There is strong need foralternative processes for the easy and effective preparation of14β-hydroxy-1,14-carbonate-deacetylbaccatine III derivatives, inparticular of compounds (I).

[0003] The process according to the invention uses as starting material10-deacetylbaccatine III which, contrary to 14β-hydroxy-baccatine III,may be easily recovered in large amounts from Taxus baccata leaves.

[0004] Therefore, the invention relates to a process for the preparationof the compounds of formula (I) which comprises the following steps:

[0005] a) protection of the hydroxyls at the 7- and 10-positions of 10deacetylbaccatine-III:

[0006] wherein R and R₁, which can be the same or different, areselected from hydrogen, C₁-C₁₀ alkyl or aryl, C₁-C₁₀ alkyl- oraryl-carbonyl, trichloroacetyl, C₁-C₄ trialkylsilyl; preferably, when Rand R₁ are the same, they are trichloroacetyl, whereas when they aredifferent, preferably R is trichloroacetyl and R₁ is acetyl, or R istriethyl or trimethylsilyl or BOC and RI is acetyl;

[0007] b) two-step oxidation to give the derivative oxidized to carbonylat the 13-position and hydroxylated at the 14-position:

[0008] c) carbonation of the vicinal hydroxyls at the 1- and14-positions to give the 1,14-carbonate derivative:

[0009] d) reduction of the carbonyl at the 13-position:

[0010] e) removal of the protective groups at the 7- and 10-positions:

[0011] f) selective acetylation of the hydroxyl at the 10-position:

[0012] g) transformation of 14β-hydroxy-baccatine-1,14-carbonate IIIinto the derivative triethylsilylated at the 7-position:

[0013] h) reaction of the compound from step (g) with(4S,5R)-N-Boc-2-(2,4-dimethoxyphenyl)-4-isobutyl-1-oxazolidine-5-carboxylicacid:

[0014] i) removal of the triethylsilyl and dimethoxybenzylideneprotective groups from the compound from step (h):

[0015] The procedures for the selective protection of the 7- and10-hydroxyls are described by Holton et al., Tetrahedron Letters 39,(1998) 2883-2886. The selective protection of the hydroxyls of thestarting compound deacetylbaccatin III is possible due to theirdifferent reactivity. In particular, the reactivity towards acylating,alkylating or silylating agents has been found to vary in the orderC(7)-OH>C(10)-OH>C(13)-OH>C(1)-OH, therefore the groups at 7- and 10-can be selectively protected while keeping the hydroxyls at 1- and 13-free. Furthermore, by changing the reaction conditions, it is possibleto reverse the reactivity order of the hydroxyls at 7- and 10- thusallowing the differential substitution thereof. Examples of reactantsand reaction conditions usable in the protection of the hydroxyls at 10-and 7- are reported in the above cited publication. Similarselectivities are obtained starting from14β-hydroxybaccatine-1,14-carbonate.

[0016] According to a preferred embodiment, deacetylbaccatine III isreacted with trichloroacetyl chloride in methylene chloride in thepresence of triethylamine and using dimethylaminopyridine (DMAP) incatalytic amounts. The use of the protective trichloroacetic groupsproved to be very advantageous in the subsequent oxidation, carbonationand reduction steps (respectively (b), (c) and (d)). In particular the7,10-bis-trichloroacetate derivative, which is obtained in quantitativeyields from the starting product, is oxidized and carbonated, theneasily reduced at the 13-position with simultaneous deprotection of thetrichloroacetic groups to give 14-hydroxy-1,14carbonate-deacetylbaccatine III. The use of DMAP in catalytic amountsprovides obvious advantages from the industrial and environmental pointof views, considering that acylations of this substrate have up to nowbeen carried out in pyridine, which involves problems of disposing ofthe residual solvent.

[0017] The oxidation step (b) of the hydroxyl at the 13-position iscarried out with manganese dioxide or bismuth dioxide or ozone in asolvent selected from acetonitrile, acetone or ethyl acetate/methylenechloride 9:1 mixtures, under vigorous stirring, preferably with ozone ormanganese dioxide in acetonitrile or acetone. The reaction with ozonerapidly forms the derivative oxidised at the 13-position, while withMnO₂ the reaction proceeds quickly to give the derivative oxidized atthe 13-position which can be recovered from the reaction medium, whereasa longer reaction yields the 13-oxidised and 14-hydroxylated derivative.

[0018] The subsequent carbonation step (c) of the hydroxyls at the 1-and 14-positions is usually effected with phosgene or in a methylenechloride/toluene mixture in the presence of pyridine. Subsequently, theresulting 1,14-carbonate derivative can be easily reduced at the13-position to give the corresponding 13-hydroxy derivative (step (d)).Said reduction takes place regioselectively at the carbonyl at 13-,while the carbonyl at 9- remains unchanged. This reaction is usuallycarried out with sodium borohydride in methanol or tetrabutylammoniumborohydride and provides high yields. The subsequent step (e) consistsin deprotecting the hydroxyls at the 7- and 10-positions to give14β-hydroxy-1,14-carbonate deacetylbaccatin III. The conditions and thereactants which can be used in the selective deprotection of thehydroxyls at 7- and. 10- are described in Zheng et al., TetrahedronLett., 1995, 36, 2001, and in Datta et al., J. Org. Chem., 1995, 60.761.

[0019] The selective acetylation at the 10-position (step (f)) iscarried out with acetic anhydride in the presence of cerium, scandium,or ytterbium salts, preferably CeCl₃₀.7H₂O. Afterwards, the hydroxyl atthe 7-position is protected by silylation (step (g)). The subsequentstep (h) involves the condensation between14β-hydroxy-7-Tes-1,14-carbonate-baccatine III and(4S,5R)-N-Boc-2-(2,4-dimethoxyphenyl)-4-isobutyl-1-oxazolidine-5-carboxylicacid. The latter is prepared as described in PCT WO 01/02407. Thereaction is carried out in dry apolar organic solvents, in the presenceof a base and of a condensation agent such as dicyclohexylcarbodiimide(DCC).

[0020] Finally, in step (i), the triethylsilyl group can be removed withpyridinium fluoride in acetonitrile/pyridine solution under nitrogen,whereas the dimethoxybenzylidene group can be removed in methylenechloride by addition of methanol HCl and subsequently of NaHCO₃.

[0021] The following examples illustrate the invention in greaterdetail.

EXAMPLE I

[0022] Preparation of 7,10-bistrichloroacetyl-10-desacetylbaccatine III.

[0023] 1^(st) Alternative:

[0024] 4.77 ml of trichloroacetic anhydride (42.32 mmoles) were droppedinto a solution of 10 g of 10-deacetylbaccatine III (18.4 mmoles) in 125ml of dry methylene chloride and 42 ml of pyridine. The reaction mixturewas kept under stirring for three hours or otherwise until completion ofthe reaction, which was monitored by TLC on silica gel using an-hexane/ethyl acetate 1:1 mixture as eluent. Upon completion of thereaction, 5 ml of methanol were added to destroy the trichloroaceticanhydride excess and then water was added. The organic phase wasthoroughly washed with water acidified with HCl to remove pyridine,while the residual organic phase was dried over MgSO₄ and concentratedto dryness under vacuum, to obtain a pale yellow solid (17 g) whichafter crystallization from chloroform has: [α]_(D)−34° (CH₂Cl₂ C5.8) IR(KBr) 3517, 1771, 1728, 1240. 981, 819, 787, 675 cm⁻¹;

[0025]¹H-NMR (200 MH): δ 8.11 (Bz C), 7.46 (Bz, BB′), 6.50 (s, H-10),5.72 (m, H-7H-29), 5.02 (d, J=8 Hz, H-5), 4.95 (8m, H-13), 4.37 (d, J=8Hz, H-20a), 4.18 (d, J=8 Hz, H-20b), 4.02 (d, J=6 Hz, H-3), 2.32 (s,4-Ac), 2.22 (s, H-18), 1.91 (s, H-19), 1.25 and 1.11 (s, H-16, H-17),1.94 (m, H14α), 1.89 (m, H14β).

[0026] 2^(nd) Alternative:

[0027] 10-DAB III (10 g, 18.38 mmol) was suspended in CH₂Cl₂ (120 ml),DMAP (220 mg, 1.4 mmol, 0.1 eqv.) was added and the mixture was cooledto 0° C. on ice bath. Then Et₃N (10.26 ml, 73.6 mmol, 4 eqv.) and,immediately after, Cl₃COCl (4.12 ml, 36.8 mmol, 2 eqv.) were added undernitrogen stream in 5 min. keeping temperature below 10° C. Aftercompletion of the addition, the mixture was left under stirring on icebath for 15 min, then the bath was removed and the mixture was stirredat r.t. for 1 h. After 1 h the reaction was monitored by TLC (AcOEt2/n-hexane 3, Rf 10-DAB III=0.05, Rf 7,10-bistrichloroacetyl-10-DABIII=0.26) and Cl₃CCOCl (1 ml, 0.5 eqv.) was added. Stirring wasmaintained at r.t. for 10 min, then the mixture was poured into a beakercontaining 160 g of triturated ice, stirring at r.t. until equilibrium(approx. 1 h). After that, the aqueous phase was separated and extractedwith CH₂Cl₂ (3×40 ml). The combined organic phases were washed with 1NHCl (20 ml), then with a NaHCO₃ saturated solution (20 ml), dried overNa₂SO₄ and the solvent was evaporated off. Crude weight: 16.5 g. Aftercrystallization from chloroform, IR, ¹H-NMR and [α]_(D) spectra wereconsistent with those of the compound obtained using pyridine andtrichloroacetic anhydride.

EXAMPLE II

[0028] Oxidation at 13- and Hydroxylation at 14- of 10-deacetylbaccatineIII 7,10-bistrichloroacetate.

[0029] To a solution of 10-deacetylbaccatine III7,10-bistrichloroacetate (3 g) in acetonitrile (40 ml), 30 g ofactivated MnO₂ were added and the suspension was magnetically stirred atroom temperature and monitored by TLC (petroleum ether-ethyl acetate5:5; Rf starting material approx. 0.31). After about one hour, theformation of the 13-dehydroderivative is complete (TLC analysis, Rf ofthe 13-dehydroderivative about 0.50). Stirring was then kept for about72 hours, during which the 13-dehydroderivative was slowly oxidized toits 14β-hydroxy derivative (Rf about 0.36). The reaction mixture wasfiltered through Celite, and the cake was repeatedly washed with ethylacetate. The solvent was evaporated off and the residue was purified bycolumn chromatography on silica gel (100 ml, eluent petroleumether-ethyl acetate 7:3) to afford 170 mg of the 13-dehydroderivativeand 1,05 g of the 14β-hydroxy-13-dehydroderivative.

[0030] 13-Dehydro-14β-hydroxy-10-deacetylbaccatin III, 7,10-bistrichloroacetate: white powder, mp 97° C.; IR (KBr disc): 3440. 1780.1767, 1736, 1686, 1267, 1232, 1103, 1010. 854 cm⁻¹;

[0031]¹H-NMR (200 MHz, CDCl₃): δ 8.07 (Bz AA′), 7.60 (Bz, C), 7.49 (Bz,BB′), 6.52 (s, H-10), 5.92 (d, J=6.7 Hz, H-2), 5.70 (br t, J=8.0 Hz,H-7), 4.95 (br d, J=8.2 Hz, H-5), 4.37 (d, J=8.2 Hz, H-20a), 4.31 (d,J=8.2 Hz, H-20b), 4.17 (s, H14), 4.02 (d, J=6.7 Hz, H-3), 2.71 (m, H-6),2.29 (s, OAc), 2.17 (s, OAc), 1.96 (s, H-18), 1.27, 1.01 (s, H-16, H-17and H-19).

EXAMPLE III

[0032] Oxidation at 13- and Hydroxylation at 14- of7-triethylsilylbaccatin III.

[0033] To a solution of 7-triethylsilylbaccatin III (1.0 g) inacetonitrile (10 ml), 10 g of activated MnO₂ were added and thesuspension was magnetically stirred at room temperature and monitored byTLC (petroleum ether-ethyl acetate 6:4; Rf starting material approx.0.25). After about 2 hours, formation of the 13-dehydroderivative wascomplete (TLC analysis, Rf 13-dehydroderivative about 0.45). Stirringwas continued for approx. 188 hours, during which additional MnO₂ (10 g)was added. The 13-dehydroderivative was slowly oxidized to its14β-hydroxy derivative (Rf about 0.38). The reaction mixture wasfiltered through Celite and the cake was washed with ethyl acetate. Thesolvent was evaporated off and the residue was purified by columnchromatography on silica gel (40 ml, eluent petroleum ether-ethylacetate 7:3) to afford 126 mg of the 13-dehydroderivative, 479 mg (46%)of 14β-hydroxy-13-dehydroderivative and 189 mg of a mixture thereof.

[0034] 13-Dehydro-7-triethylsilylbaccatin III. White powder, mp 168° C.[α]_(D) ²⁵−35 (CH₂Cl₂, C 0.67) IR (KBr) 3488, 1726, 1711, 1676, 1373,1269, 1244, 1230. 1105 cm⁻¹; ¹H-NMR (200 MH CDCl₃): δ 8.07 (Bz AA′),7.60 (Bz, C), 7.49 (Bz, BB′), 6.59 (s, H-10), 5.69 (d, J=6.9 Hz, H-2),4.92 (d, J=8.2 Hz, H-5), 4.48 (dd, J=10.6 Hz, H-7), 4.33 (d, J=8.0 Hz,H-20a), 4.12 (d, J=8.0 Hz, H-20b), 3.91, (d, J=6.9 Hz, H-3), 2.96 (d,J=20 Hz, H-14a), 2.65 (d, J=20 Hz, H-20b), 2.50 (m, H-6α), 2.23 (s,OAc), 2.19 (s, OAc+H-18), 1.67, 1.28, 1.19 (s, H-16, H1-17 and H-19),0.19 (m, TES).

[0035] 13-Dehydro-14β-hydroxy-10-deacetylbaccatin III, 7,10-bistrichloroacetate: white powder, mp 153° C. [α]_(D) ²⁵+20 (CH₂Cl₂, C0.75) IR (KBr) 3431, 1723, 1692, 1371, 1269, 1242, 1223, 1096 cm⁻¹;¹H-NMR (500 MH CDCl₃): δ 8.06 (Bz AA′), 7.60 (Bz, C), 7.48 (Bz, BB′),6.51 (s, H-10), 5.88 (d, J=6.9 Hz, H-2), 4.90 (d, J=8.2 Hz, H-5), 4.47(dd, J=10.67 Hz, H-7), 4.30 (d, J=8 Hz, H-20a), 4.28 (d, J=8.2 Hz,H-20b), 4.13 (br d, J=2 Hz, H-14), 3.84 (d, J=6.9 Hz, H-3), 3.69 (br d,J=2 Hz, 14-OH), 3.62 (s, 1-OH), 2.52 (m, H-6β), 2.24 (s, OAc), 2.21 (s,OAc), 2.11 (s, H-18), 1.92(m, H-6α), 1.74, 1.56, 1.28 (s, -h-16, H-17and H-19), 0.94 (m, TES), 0.59 (m, TES). HRNS: 714.3092 (calculated forC₃₇H₅₀O₁₂Si 714.3092).

EXAMPLE IV

[0036] Preparation of1,14-carbonate-13-dehydro-7-TES-14β-hydroxy-baccatine III.

[0037] To a solution of phosgene (1.8 ml of a 20% solution in toluene,3.4 mmol, 20 mol. equiv.) and pyridine (0.56 ml, 6,8 mmol, 20 mol.equiv.) in CH₂Cl₂ (2 ml), a solution of13-dehydro-14β-hydroxy-7-triethylsilylbaccatin III (124 mg, 1,17 mmol)in CH₂Cl₂ (1 ml) was added dropwise in 5 min. The mixture was stirred atroom temperature for 1 hour, subsequently quenching the excess phosgeneby addition of a NaHCO₃ saturated solution and extraction with CH₂Cl₂.The organic phase was washed with a NaHCO₃ saturated solution, brine,and dried (Na₂SO₄). The solvent was evaporated off to yield a reddishresidue, which was purified on a short silica gel column (about 5 ml,eluent hexane/ethyl acetate 8:2) to afford 118 mg (92%) of thecarbonate. If the reaction is carried out using with triethylamine asthe base and without inverse addition, an about 1:15 mixture of1,14-cabonate and 2-debenzoyl-1,2-carbonate-14 benzoate is obtained.

[0038] 13-Dehydro-14β-hydroxy-7-triethylsilylbaccatin III1,14-carbonate. White powder, mp 153° C. [α]_(D) ²⁵+23 (CH₂Cl₂, C 0.75)IR (KBr) No. of OH band 1834, 1734, 1709, 1373, 1242, 1225, 1088, 1057cm; ¹H-NMR (200 MH CDCl₃): β 7.99 (Bz AA′), 7.60 (Bz, C), 7.48 (Bz,BB′), 6.51 (s, H-10), 6.12 (d, J=6.9 Hz, H-2), 4.90 (d, J=8.2 Hz, H-5),4.78 (s, H-14), 4.44 (dd, J 10.7 Hz, H-7), 4.34 (d, J=8 Hz, H-20a), 4.19(d, J=8.2 Hz, H-20b), 3.80 (d, J=6.9 Hz, H-3), 2.50 (m, H-6α), 2.23 (s,OAc), 2.22 (s, OAc), 2.19 (s, H-18), 1.92 (m, H-6α), 1.72, 1.39, 1.26(s, -H-16, H-17 and H-19), 0.90 (m, TES), 0.56 (m, TES). HRNS: 740.2851(calculated for C₃8H₄₈O₁₃Si 740.2864).

[0039] 13-Debydro-14β-hydroxybaccatine III 1,14-carbonate. White powder240° C. [α]_(D) ²⁵−2.5 (CH₂Cl₂, C 0.4) IR (KBr) 3539, 1831, 1736, 1240,1088, 1068, 1057, 1024 cm⁻¹; ¹H-NMR (200 MH CDCl₃): δ 7.98 (Bz AA′),7.61 (Bz, C), 7.50 (Bz, BB′), 6.39 (s, H-10), 6.14 (d, J=6.9 Hz, H-2),4.98 (d, J=8.2 Hz, H-5), 4.80 (s, H-14), 4.43 (dd, J=10.7 Hz, H-7), 4.35(d, J=8 Hz, H-20a), 4.24 (d, J=8.2 Hz, H-20b), 3.80 (d, J=6.9 Hz, H-3),2.50 (m, H-6β), 2.30 (s, OAc), 2.20 (s, OAc), 2.15 (s, H-18), 1.90 (m,H-6β), 1.74, 1.34, 1.25 (s, H-16, H-17 and H-19), HRMS: 626.2005(calculated for C₃₃H₃₄O₁ 626.1999).

EXAMPLE V

[0040] Preparation of 1,14-carbonate-7-O-triethylsilyl Baccatine III.

[0041] To a solution of 13-dehydro-14β-hydroxy-7-triethylsilylbaccatinIII

[0042] 1,14-carbonate (50 mg) in methanol (5 ml), an excess NaBH₄ (about20 mg) was added in small portions. After 30 min, the reaction mixturewas added with saturated NH₄Cl, extracted with ethyl acetate, washedwith brine and dried over Na₂SO₄. The solvent was evaporated off and theresidue was purified by column chromatography on silica gel (about 5 ml,elution with hexane-ethyl acetate 8:2) to afford 35 mg of the13α-hydroxy derivative and 9 mg of the 13β-hydroxy derivative.

[0043] 14β-Hydroxy-7-triethylsilylbaccatin III 1,14-carbonate [α]_(D)²⁵35 (CH₂Cl₂, C 0.60) IR (KBr) 3054, 1819, 1736, 1603, 1371, 1261, 1238,1090. 1069, cm⁻¹; ¹H-NMR (200 MH CDCl₃): δ 8.06 (Bz AA′), 7.65 (Bz, C),7.50 (Bz, BB′), 6.47 (s, H-10), 6.12 (d, J=6.9 Hz, H-2), 5.05 (br d,J=5.5 Hz, H-13), 4.98 (br d, J=9 Hz, H-5), 4.83 (d, J=5 Hz, H-14), 4.50(dd, J=10.7 Hz, H-7), 4.34 (d, J=8 Hz, H-20a), 4.23 (d, J=8 Hz, H-20b),3.75 (d, J=6.9 Hz, H-3), 2.56 (m, H-6O), 2.34 (s, OAc), 2.22 (s, OAc),1.78 (m, H-6β), 1.35 (s, H-18), 1.75, 1.18, 0.95 (s, -H-16, H-17 andH-19), 0.90 (m, TES), 0.62 (m, TES).

[0044] 14β-Hydroxy-7-triethylsilyl-13-epibaccatine III 1,14-carbonate.Amorphous, [α]_(D) ²⁵−13 (CH₂Cl₂, C 0.60) IR (KBr) 3630. 1825, 1734,1603, 1375, 1262, 1091, 1071, 1049 cm⁻¹; 1H-NMR (200 MH CDCl₃): δ 8.01(Bz AA′), 7.63 (Bz, C), 7.48 (Bz, BB′), 6.44 (s, H-10), 6.12 (d, J=7.2Hz, H-2), 4.90 (br d, J=9 Hz, H-5), 4.81 (d, J=8 Hz, H-14), 4.48 (br,J=8, H-13), 4.50 (dd, J=10. 7 Hz, H-7), 4.41 (d, J=8 Hz, H-20a), 4.31(d, J=8 Hz, H-20b), 3.68 (d, J=7.2 Hz, H-3), 2.60 (m, H-6β), 2.32 (s,OAc), 2.26 (s, H-18), 2.21 (s, OAc), 1.80 (m, H-6α), 1.72, 1.43, 1.27(s, -H-16, H-17 and H-19), 0.93 (m, TES), 0.61 (m, TES).

EXAMPLE VI

[0045] Preparation of13-dehydro-14β-hydroxy-7,10-bistrichloroacetyl-baccatine III1,14-carbonate.

[0046] A solution of13-dehydro-14β-hydroxy-7,10-bistrichloroacetyl-baccatine III (200 mg) inCH₂Cl₂ (2 ml) was added in 5 min to a solution of phosgene (20% intoluene, 3.6 ml, 20 equiv.) and pyridine (1.12 ml, 20 equiv.) in CH₂Cl₂(2 ml). The mixture was stirred at r.t. for 1 h, then the excessphosgene was quenched with a NaHCO₃ saturated solution (3 ml). Themixture was extracted with CH₂Cl₂, the organic portion was washed with aNaHCO₃ saturated solution, then with a NaCl saturated solution and driedover Na₂SO₄. The solvent was evaporated off and the residue was purifiedby column chromatography on silica gel (eluent hexane/AcOEt 9:1) toafford 175 mg (89%) of the carbonate.

[0047] 13-Dehydro-14β-hydroxy-7,10-bistrichloroacetyl-baccatine III1,14-carbonate. White amorphous solid. IR (KBr) 1834, 1771, 1735, 1709,1232, 1103, 1010, 854 cm⁻¹.

[0048]¹H-NMR (200 MHz, CDCl₃): δ=8.03 (Bz AA′), 7.60 (Bz, C), 7.50 (Bz,BB′), 6.52 (s, H-10), 5.92 (d, J=6.7 Hz, H-2), 5.70 (br t, J=8.0 Hz,H-7), 4.95 (br d, J=8.2 Hz, H-20b), 4.77 (s, H-14), 4.02 (d, J=6.7 Hz,H-3), 2.71 (m, H-6), 2.29 (s, OAc), 1.96 (s, H-18),1.27-1.01 (m, H-16,H-17, H-19).

EXAMPLE VII

[0049] Preparation of 14β-hydroxy-10-deacetylbaccatine III1,14-carbonate.

[0050] A solution of13-dehydro-14β-hydroxy-7,10-bistrichloroacetyl-baccatine III1,14-carbonate (500 mg) in MeOH (8 ml) was cooled to 0° C. on ice bathand solid NaBH₄ (44 mg) was added thereto in 5 min. The mixture wasstirred at r.t. for 1 h, then cooled to 0° C., added with acetone (2 ml)in 5 min and concentrated under mild vacuum, then added with AcOEt (10ml) and filtered through Celite. The clear solution was washed with aNaCl saturated solution and dried over Na₂SO₄. The solvent wasevaporated off, the residue (4.5:1 mixture of C13 epimers) was purifiedby chromatography on a silica gel column (eluent hexane/AcOEt 1:1) toafford 251 mg of the title compound and 55 mg of the 13-epimer,(88%total) of the deprotected carbonate.

[0051] 14β-Hydroxy-10-deacetylbaccatine III 1,14-carbonate. Whiteamorphous solid. IR (KBr): 3520 (OH), 1834, 1709, 1232, 1103, 1010, 854cm⁻¹.

[0052]¹H-NMR (200 MHz, CDCl₃): δ=8.03 (Bz AA′), 7.60 (Bz, C), 7.50 (Bz,BB′), 6.27 (s, H-10), 5.92 (d, J=6.7 Hz, H-2), 4.95 (br d, J=8.2 Hz,H-20b), 4.85 (m, H-13), 4.77 (s, H-14), 4.42 (br t, J=8.0 Hz, H-7), 4.02(d, J=6.7 Hz, H-3), 2.71 (m, H-6), 2.29 (s, OAc), 1.96 (s, H-18),1.27-1.01 (m, H-16, H-17, H-19).

EXAMPLE VIII

[0053] Preparation of 13-(N-Boc-β-isobutylserinyl)-14β-hydroxybaccatineIII 1,14-carbonate.

[0054] To a solution of 14β-hydroxy-10-deacetylbaccatin III1,14-carbonate (126 mg) in 3 ml of dry tetrahydrofuran, 7.5 mg ofCeCl₃₀.7H₂O and 0.078 ml of acetic anhydride were added. The reactionmixture was kept under stirring at room temperature for 5 h. duringwhich the reaction mixture became homogeneous. 1.5 g of ice were added,keeping stirring for 1 h. The organic solvent was evaporated off undervacuum and the residue was diluted with 5 ml of H₂O. The formedprecipitate was filtered and dried by suction for 18 h. The resultingproduct (white powder, 135 mg) has the following characteristics:

[0055]¹H-NMR (400 MHz, CDCl₂). δ_(ppm)=1.25, 1.11 (s, H-16 and H-17),1.66 (s, H-19), 2.04 (s, H-18), 2.22 (s, OAc), 2.29 (s, OAc), 3.89 (d,J=0.9 Hz, H-3), 4.06 (d, J=7 Hz, C20b), 4.20 (d, J=7 Hz, H20a), 4.41 (m,H-7), 4.77 (d, J=4 Hz, H-14), 4.85 (br d, J=4 Hz, H-13), 4.97 (br d, J=8Hz, H-5), 5.8 (d, J=7 Hz, H-2), 6.31 (s, H-10), 7.44 (t, J (Hz, Bz),7.55 (d, J=8 Hz, Bz), 8.07 (d, J=8 Hz, Bz).

[0056] 14β-Hydroxybaccatine III 1,14-carbonate (130 mg) was dissolved indimethylformamide (4 ml) and N-methylimidazole (0.07 ml) was added.Triethylchlorosilane (0.042 ml) was added to the solution under strongstirring at room temperature in 1 h. The mixture was then poured into 10ml of H₂O under strong stirring. The suspension was left at 4° C. for 18h and the formed white precipitate was filtered off and washed with H₂O(5 ml), then with hexane (2×3 ml). The resulting white solid (150 mg)has the same spectroscopical characteristics as those of the compoundprepared in Example V.

[0057] In a III round-bottom flask, 20 g of14β-hydroxy-7-Tes-1,14-carbonate-baccatine III were placed together with300 ml of rigorously dry toluene; then 10 g of(4S,5R)-N-Boc-2-(2,4-dimethoxyphenyl)-4-isobutyl-1-oxazolidine-5-carboxylicacid, 2 g of N,N-dimethylaminopyridine (DMAP) and 9.5 g ofdicyclohexylcarbodiimide (DCC) dissolved in CH₂Cl₂ were added. Thereaction mixture was refluxed for 3 h, then cooled and the precipitatedureic product was removed. Mother liquors were washed with a NaHCO₃saturated solution to remove the unreacted acid, then with dilutedhydrochloric acid to remove DMAP, then again with NaHCO₃ to neutrality.The organic phase was concentrated to dryness to obtain 41.5 g ofproduct which can be used as such in the subsequent step. 40 g of thiscompound were deprotected in two steps, by removing first Tes and then2,4-dimethoxybenzaldehyde. 40 g of the compound were dissolved in 100 mlof an acetonitrile/pyridine mixture (80:100) under nitrogen and themixture is cooled to 0° C., then added with 13 ml of pyridinium fluorideand left under stirring for 24 h. The solution was poured into 2 l ofwater and the product was filtered and dried under vacuum.

[0058] The residue was dissolved in 60 ml of methylene chloride and thissolution was kept under strong stirring at 0° C. and added with 40 ml of0.6N methanol HCl. The reaction mixture was left under stirring for 2hr, then diluted with 150 ml of methylene chloride and agitated with aNaHCO₃ solution, adjusting pH to 6-7. The organic phase was concentratedto dryness and the residue was crystallized from acetone hexane anddried to obtain 16 g of13-(N-Boc-β-isobutylisoserinyl)-14β-hydroxybaccatine-1,14-carbonatehaving the following physico-chemical and spectroscopicalcharacteristics:

[0059] Formula: C₄₄H₅₇NO₁₇

[0060] Aspect: white powder.

[0061] Melting point: 245° C. TABLE 1 Chemical shifts (ppm) ¹H-NMR inCDCl₃ solution (200 MHz) H Ppm, multiplicity (Hz) H Ppm, multiplicity(Hz)  2 6.09-d (7.8)  2′ 4.30-dd (6.4; 3.2)  3 3.68-d (7.4)  3′ 4.08-m 5 4.91-dd (9.7; 2.5)  4′a 1.21-m  6α 2.52-ddd (14.8; 9.8; 6.9)  4′b1.43-m  6β 1.86-m  5′ 1.65-m  7 4.37-m  6′ 0.96-d (6.3) 10 6.25-s  7′0.95-d (6.3) 13 6.44-d (broad, 6.9)  4-OCOCH₃ 2.40-s 14 4.84-d (6.9)10-OCOCH₃ 2.22-s 16 1.25-s Boc 1.35-s 17 1.32-s o-benzoyl 8.01-m 181.87-d (1.6) m-benzoyl 7.46-m 19 1.69-s p-benzoyl 7.58-m 20α 4.27-d(8.4)  3′-NH 4.72-d (9.0) 20β 4.20-d (8.4)

[0062] TABLE 2 Chemical shifts (ppm) ¹³C NMR in CDCl₃ solution (50.308MHz) C ppm, multiplicity C ppm, multiplicity  9 201.8-s  8  58.2-s  1′172.6-s  3′  51.2-d  4-OCOCH₃ 170.5-s  3  44.6-d 10-OCOCH₃ 170.2-s 15 41.3-s  2-COPh 164.3-s  4′  39.9-t C═O (Boo) 155.8-s  6  34.9-t C═O(carbonate) 151.4-s (CH₃)₃C Boc  27.7-q 12 139.4-s 17  25.5-q 11 133.1-s16  22.6-q (Me)₃ C(Boc)  80.0-s  4-OCOCH₃  22.0-q  5  83.8-d 10-OCOCH₃ 20.2-q  1  87.7-s  5′  24.3-d  4  80.0-s  6′  22.7-q  2  69.0-d  7′ 21.6-q 20  75.5-t 18  14.6-q  2′  73.3-d 19  9.8-q  7  71.2-d q-benzoyl127.5-s 10  74.3-d o-benzoyl 129.5-d 13  74.1-d m-benzoyl 128.6-d 14 79.1-d p-benzoyl 133.7-d

[0063] Mass spectra: (NH₃, DEP/CI, positive ions): (m/z) 889 [(MNH₄)⁺],832 [(MNH₄—(CH₃)₃C)⁺], 772 [(MNH₄-BocNH₂)⁺]

[0064] (NH₃, DEP/CI, negative ions): (m/z) 871 (M⁻¹), 260 (side chain)

[0065] Infrared spectrum (KBr pellet): 3521, 3321, 2971, 2953, 1826,1762, 1706, 1526, 1366, 1238, 1165, 1072, 723 cm⁻¹

[0066] UV spectrum (MeOH): 231, 276 and 284 nm;

[0067] E_(1%) at 231 nm=180.99

[0068] E_(1%) at 276 nm=14.094

[0069] E_(1%) at 284 nm=12.182

1. A process for the preparation of the compound13-(N-Boc-β-isobutylisoserinyl)-14β-hydroxybaccatine III 1,14-carbonate,of formula (I)

which comprises: a) protection of the hydroxyls at the 7- and10-positions of 10 deacetylbaccatine III:

wherein R and R₁, which can be the same or different, are selected fromhydrogen, C₁-C₁₀ alkyl or aryl, C₁-C₁₀ alkyl- or aryl-carbonyl,trichloroacetyl, C₁-C₄ trialkylsilyl; b) two-step oxidation to give thederivative oxidized to carbonyl at the 13-position and hydroxylated atthe 14-position:

c) carbonation of the vicinal hydroxyls at the 1- and 14-positions togive the 1,14-carbonate derivative:

d) reduction of the carbonyl at the 13-position:

e) removal of the protective groups at the 7- and 10-positions:

f) selective acetylation of the hydroxyl at the 10-position:

g) transformation of 14β-hydroxy-baccatine-1,14-carbonate III into thederivative triethylsilylated at the 7-position:

h) reaction of the compound from step (g) with(4S,5R)-N-Boc-2-(2,4-dimethoxyphenyl)-4-isobutyl-1-oxazolidine-5-carboxylicacid:

i) removal of the triethylsilyl and dimethoxybenzylidene protectivegroups from the compound from step (h):


2. A process as claimed in claim 1, wherein R=R₁=trichloroacetyl.
 3. Aprocess as claimed in claim 1, wherein R and R₁ are different and R istrichloroacetyl and R₁ acetyl, or R is triethyl or trimethylsilyl and R₁is acetyl.
 4. A process as claimed in claim 1, wherein deprotection step(a) of the hydroxyls at the 7- and 10-positions is carried out withtrichloroacetyl chloride in methylene chloride in the presence oftriethylamine and of catalytic amounts of dimethylaminopyridine.
 5. Aprocess as claimed in claim 1, wherein step (b) of oxidation of thehydroxyl at the 13-position and hydroxylation at the 14-position iscarried out with manganese dioxide or bismuth dioxide or ozone in asolvent selected from acetonitrile, acetone or an ethylacetate/methylene chloride mixture.
 6. A process as claimed in claim 1,wherein carbonation step (c) of the hydroxyls at the 1- and 14-positionsis carried out with phosgene in a methylene chloride/toluene mixture inthe presence of pyridine.
 7. A process as claimed in claim 1, whereinreduction step (d) to 13-hydroxy is carried out with sodium borohydridein methanol.
 8. A process as claimed in claim 1, wherein acetylationstep (f) of the hydroxyl at the 10-position is carried out with acetylchloride.
 9. A process as claimed in claim 8, wherein the silylationstep (g) is carried out with triethylchlorosilane.
 10. A process asclaimed in claim 1, wherein the reaction step (h) is carried out in dryapolar organic solvents, in the presence of a base and of thecondensation agent dicyclohexylcarbodiimide (DCC).
 11. A process asclaimed in claim 1, wherein the triethylsilyl protective group isremoved in step (i) with pyridinium fluoride in acetonitrile/pyridinesolution under nitrogen, and the dimethoxybenzylidene protective groupis removed in methylene chloride solvent by addition of methanol HCl andsubsequently of NaHCO₃.